1. FIELD OF THE INVENTION
This invention concerns methods of manufacturing headers and more particularly a method of cold forming header assemblies without brazing or welding.
2. DESCRIPTION OF THE PRIOR ART
Due to the upward trend in cost of the copper metal which has been widely used in manufacturing finned tube heat exchangers such as are used in refrigeration and air conditioning systems, efforts have been periodically exerted to reduce the quantity of copper used in such assemblies. As a result of these efforts, the use of lower cost aluminum has progressively become more extensive, such as the use of aluminum fins on copper tubings. Aluminum has also been used extensively in the tubing portions thereof but has suffered from some disadvantages in manufacturing techniques required over those required with copper. Specifically, difficulties are encountered in the brazing of aluminum such as is required in current manufacturing methods for forming header assemblies, i.e. assemblies in which a plurality of tubes transition into a common header passage. These difficulties arise as a result of the tendency of aluminum to form surface oxides, requiring the use of fluxes which are relatively corrosive to the aluminum, so that rather extensive cleaning operations must be performed after the brazing operations. In addition, the brazed joints in such assemblies are difficult to make with great reliability so that such joints account for high percentage of the leakage failures of such assemblies. This arises in part because header joints, being non-linear, cannot be made with the use of continuous automated equipment, which factor also contributes to the relatively high costs of this process.
Alternative forming methods such as disclosed in the U.S. Patents granted to Charles True, U.S. Pat. No. 1,264,455; to Charles True and N.T. McKee, U.S. Pat. No. 1,169,209; to Charles True and C.W. Brandt, U.S. Pat. No. 1,255,355, to B. Broido, U.S. Pat. No. 1,331,047; to T.F. Birmingham, U.S. Pat. No. 1,503,469; to A. Magis, U.S. Pat. No. 1,678,740; and to G.E. Ryder, U.S. Pat. No. 1,471,944 all describe an approach to forming such a header assembly by splitting a plurality of tubes positioned in a female die by means of a male forming member. This approach necessarily splits the walls of the tubes and requires heating and welding of the split portions in order to form a fluid tight header section. It can be appreciated that this necessity for heating to welding temperatures results in a relatively expensive form of manufacture and in addition, the necessity of forming good welds reduces the reliability of the resultant structure, particularly for aluminum.
Yet another approach which involves a brazing operation is disclosed in U.S. Pat. No. 2,927,369 to W. H. Coblantz et al. In this method, corrugated rolled strips are brazed together to form the tube bundle with the header section formed integral therewith but this method suffers from the disadvantages aforementioned in regard to the brazing of aluminum.
Other possible methods of cold forming such sections generally would involve relatively expensive mandril extrusion processes, which would limit the length of the header sections and also require relatively extensive capital equipment.
It is therefore an object of the present invention to provide a cold forming method for forming a header section which does not involve the use of extensive capital equipment and tooling and eliminates the need for welding and brazing operations.